This Week in Science

Science  24 May 1996:
Vol. 272, Issue 5265, pp. 1077
  1. Atomic realization of Schrödinger's cat

    In quantum mechanics, microscopic states can be combined in superpositions that may defy our classical view of reality. In a famous thought experiment, “Schrödinger's cat” was placed in a sealed box with a radioactive decay experime nt, the result of which determines whether the cat lives or dies. Strictly speaking, even after the detector records the decay event, we cannot say the cat is alive or dead; we can only give a probability. In an effort to better understand this aspect of quantum mechanics, Monroe et al.(p. 1131; see the news story by Taubes, p. 1101) have constructed an atomic system (a l aser-cooled beryllium ion held in a harmonic oscillator potential) that can entangle the electronic and motional states of the atom in a manner analogous to Schrödinger's cat. Such systems can be used to study quantum decoherence, the evolution of th ese states into statistical mixtures.

  2. Assembly lines


    The self-assembly of amphiphilic molecules on surfaces into highly ordered films couldfind applications that include biosensors and corrosion inhibitors. Poirier and Pylant ( p. 1145); see the Perspective by Chiang, p. 1123) investigated the assembly mechanism of such monolayers by scanning tunneling microscopy and observed a two-step growth mode. A phase transition to a denser phase occurred as coverage increased.

  3. Older hoofed order

    Orders of ungulates (hoofed mammals) have been recognized back to the early Tertiary (about 65 million years ago). In a phylogenetic analysis, Archibald (p. 1150); see the news story by Peterson, p. 1102), now suggests that they can be related back to fossils primarily from the 85 million-year-old Bissekty Formation, Uzbekistan. These fossil deposits may mark the beginning of herbivory in placental mammals.

  4. Ocean carbon control

    The ocean surface is home to much biologic activity, including the incorporation of atmospheric CO2 into biomass by means of photosynthesis. A portion of the biogenic carbon is then exported to ocean depths. Rivkin et al.( p. 1163) show that, in the Gulf of St. Lawrence, biogenic carbon export was similar from both herbivorous and omnivorous food webs and was not directly proportional to new photosynthetic production, which can increase dramatically during spring bloom. Models predicting the amount and nature of biogenic carbon transport may need to rely on other parameters.

  5. Collecting copper

    Some of the world's richest copper deposits were formed at low temperatures when descending fluids dissolved, and then concentrated copper minerals originally formed in magmatic hydrothermal systems, a process called supergene enrichment. Sillitoe et al.(p. 1153) now provide morphological evidence—essentially metallized bacterial fossils—that bacteria were involved in supergene enrichment in copper deposits in northern Chile and may have facilitated copper fixation at depth.

  6. Going for the Golgi

    Vesicles and organelles must have address tags that control the budding and fusion events of intracellular transport. Subramaniam et al. (p. 1161) identified a cis-Golgi membrane protein that acts as one of the targeting receptors. The protein is thought to be involved in the recognition of vesicles derived from the endoplasmic reticulum that must fuse with the cis-Golgi.

  7. Tapping the TGF-β receptor

    Transforming growth factor-beta (TGF-beta regulates functions of many different cell types and has potential therapeutic applications, but the way in which signals are transmitted from the TGF-beta receptor are not well understood. This receptor, itself a serine threonine kinase, activates a member of the mitogen-activated protein kinase kinase kinase (MAPKKK) family that is known as TAK1. MAPKKKs activate a series of protein ki nases and thus carry signals from various receptors on the cell surface to the nucleus. Shibuya et al.(p. 1179) identified a new protein, TAB1, that interacts with the MAPKKK and tha t is not related to any known protein. TAB1 appears to participate in activation of TAK1 by TGF-beta and to provide a new mechanism by which members o f a MAP kinase cascade can be activated.

  8. Regulating antigen signaling

    When antigens activate the T cell receptor (TCR), they initiate the immune response (T cell proliferation) by triggering tyrosine phosphorylation within the cell. Two reports show that negative regulation of kinase activity by phosphatases is initiated as well. Marengère et al. (p. 1170) show that CTLA-4, whose surface expression increases after TCR activation, is associated with the tyrosine phosphatase SYP. The CTLA-4-associated SYP can down-regulate both the TCR and the RAS pathways. Plas et al.(p. 1173) show that T cell activation causes the binding of the tyrosine phosphatase SHP-1 to the tyrosine kinase ZAP-70. This kinase is stimulated by TCR activation but SHP-1 binding decreases its activity.

  9. Cryptic origins

    Cancers are generally thought to be monoclonal in origin, that is, to arise from a single mutant cell and its descendants. Novelli et al.(p. 1187) have tested this hypothesis by studying a rare patient who was an XO/XY mosaic and who also had familial adenomatous polyposis, a disorder characterized by the development of multiple precancerous microadenomas in the colon. In situ hybridization studies of tissue sections with Y chromosome-specific probes revealed that intestinal crypts were monoclonal in origin, but surprisingly the majority of microadenomas were polyclonal in origin.